Polyphasic evidence for the reclassification of Rhodothermus obamensis Sako et al. 1996 as a member of the species Rhodothermus marinus Alfredsson et al. 1988

Rhodothermus bifroesti sp. nov., a thermophilic bacterium isolated from the basaltic subsurface of the volcanic island Surtsey

Novel thermophilic heterotrophic bacteria were isolated from the subsurface of the volcanic island Surtsey off the south coast of Iceland. The strains were isolated from tephra core and borehole fluid samples collected below 70 m depth. The Gram-negative bacteria were rod-shaped (0.3-0.4 µm wide, 1.5-7 µm long), aerobic, non-sporulating and non-motile. Optimal growth was observed at 70 °C, at pH 7-7.5 and with 1% NaCl. Phylogenetic analysis identified the strains as members of the genus Rhodothermus. The type strain, ISCAR-7401^T, was genetically distinct from its closest relatives Rhodothermus marinus DSM 4252^T and Rhodothermus profundi PRI 2902^T based on 16S rRNA gene sequence similarity (95.81 and 96.01%, respectively), genomic average nucleotide identity (73.73 and 72.61%, respectively) and digital DNA-DNA hybridization (17.6 and 16.9%, respectively). The major fatty acids of ISCAR-7401^T were iso-C_17:0, anteiso-C_15:0, anteiso-C_17:0 and iso-C_15:0 (>10 %). The major isoprenoid quinone was MK-7 while phosphatidylethanolamine, diphosphatidylglycerol, an unidentified aminophospholipid and a phospholipid were the predominant polar lipid components. Based on comparative chemotaxonomic, genomic and phylogenetic analyses, we propose that the isolated strain represents a novel species of the genus Rhodothermus with the name Rhodothermus bifroesti sp. nov. The type strain is ISCAR-7401^T (=DSM 112103^T=CIP 111906^T).

Raineya orbicola gen. nov., sp. nov. a slightly thermophilic bacterium of the phylum Bacteroidetes and the description of Raineyaceae fam. nov

An isolate, designated SPSPC-11T, with an optimum growth temperature of about 50 °C and an optimum pH for growth between 7.5 and 8.0, was recovered from a hot spring in central Portugal. Based on phylogenetic analysis of its 16S rRNA sequence, the new organism is most closely related to the species of the genus Thermonema but with a pairwise sequence similarity of <85 %. The isolate was orange-pigmented, formed non-motile long filaments and rod-shaped cells that stain Gram-negative. The organism was strictly aerobic, oxidase-positive and catalase-positive. The major fatty acids were iso-C15:0, iso-C15 : 0 2-OH and iso-C17 : 0 3-OH. The major polar lipids were one aminophospholipid, two aminolipids and three unidentified lipids. Menaquinone 7 was the major respiratory quinone. The DNA G+C content of strain SPSPC-11T was 37.6 mol% (draft genome sequence). The high quality draft genome sequence corroborated many of the phenotypic characteristics of strain SPSPC-11T. Based on genotypic, phylogenetic, physiological and biochemical characterization we describe a new species of a novel genus represented by strain SPSPC-11T (=CECT 9012T=LMG 29233T) for which we propose the name Raineya orbicola gen. nov., sp. nov. We also describe the family Raineyaceae to accommodate this new genus and species.

Genome Analysis of a New Rhodothermaceae Strain Isolated from a Hot Spring

A bacterial strain, designated RA, was isolated from water sample of a hot spring on Langkawi Island of Malaysia using marine agar. Strain RA is an aerophilic and thermophilic microorganism that grows optimally at 50–60°C and is capable of growing in marine broth containing 1–10% (w/v) NaCl. 16S rRNA gene sequence analysis demonstrated that this strain is most closely related (<90% sequence identity) to Rhodothermaceae, which currently comprises of six genera: Rhodothermus (two species), Salinibacter (three species), Salisaeta (one species), Rubricoccus (one species), Rubrivirga (one species), and Longimonas (one species). Notably, analysis of average nucleotide identity (ANI) values indicated that strain RA may represent the first member of a novel genus of Rhodothermaceae. The draft genome of strain RA is 4,616,094 bp with 3630 protein-coding gene sequences. Its GC content is 68.3%, which is higher than that of most other genomes of Rhodothermaceae. Strain RA has genes for sulfate permease and arylsulfatase to withstand the high sulfur and sulfate contents of the hot spring. Putative genes encoding proteins involved in adaptation to osmotic stress were identified which encode proteins namely Na⁺/H⁺ antiporters, a sodium/solute symporter, a sodium/glutamate symporter, trehalose synthase, malto-oligosyltrehalose synthase, choline-sulfatase, potassium uptake proteins (TrkA and TrkH), osmotically inducible protein C, and the K⁺ channel histidine kinase KdpD. Furthermore, genome description of strain RA and comparative genome studies in relation to other related genera provide an overview of the uniqueness of this bacterium.

Molecular and lipid biomarker analysis of a gypsum-hosted endoevaporitic microbial community

Modern evaporitic microbial ecosystems are important analogs for understanding the record of earliest life on Earth. Although mineral-depositing shallow-marine environments were prevalent during the Precambrian, few such environments are now available today for study. We investigated the molecular and lipid biomarker composition of an endoevaporitic gypsarenite microbial mat community in Guerrero Negro, Mexico. The 16S ribosomal RNA gene-based phylogenetic analyses of this mat corroborate prior observations indicating that characteristic layered microbial communities colonize gypsum deposits world-wide despite considerable textural and morphological variability. Membrane fatty acid analysis of the surface tan/orange and lower green mat crust layers indicated cell densities of 1.6 × 10(9) and 4.2 × 10(9)  cells cm(-3) , respectively. Several biomarker fatty acids, ∆7,10-hexadecadienoic, iso-heptadecenoic, 10-methylhexadecanoic, and a ∆12-methyloctadecenoic, correlated well with distributions of Euhalothece, Stenotrophomonas, Desulfohalobium, and Rhodobacterales, respectively, revealed by the phylogenetic analyses. Chlorophyll (Chl) a and cyanobacterial phylotypes were present at all depths in the mat. Bacteriochlorophyl (Bchl) a and Bchl c were first detected in the oxic-anoxic transition zone and increased with depth. A series of monomethylalkanes (MMA), 8-methylhexadecane, 8-methylheptadecane, and 9-methyloctadecane were present in the surface crust but increased in abundance in the lower anoxic layers. The MMA structures are similar to those identified previously in cultures of the marine Chloroflexus-like organism 'Candidatus Chlorothrix halophila' gen. nov., sp. nov., and may represent the Bchl c community. Novel 3-methylhopanoids were identified in cultures of marine purple non-sulfur bacteria and serve as a probable biomarker for this group in the lower anoxic purple and olive-black layers. Together microbial culture and environmental analyses support novel sources for lipid biomarkers in gypsum crust mats.

Schleiferia thermophila gen. nov., sp. nov., a slightly thermophilic bacterium of the phylum ‘Bacteroidetes’ and the proposal of Schleiferiaceae fam. nov

A bacterial isolate, with an optimum growth temperature of about 50 °C and an optimum pH for growth between 7.5 and 8.5, was recovered from a hot spring in the Furnas area of the Island of São Miguel in the Azores. The novel isolate is orange-pigmented, forms non-motile, rod-shaped cells that stain Gram-negative, is strictly aerobic, oxidase-positive and catalase-negative. The major fatty acids of strain TU-20T are 16 : 1ω6c, 17 : 0 iso 3-OH and 15 : 0 iso. Menaquinone 6 is the major respiratory quinone. Based on 16S rRNA gene sequence analysis, physiological and biochemical characteristics, we describe a novel species of a novel genus represented by strain TU-20T ( = DSM 21410T  = LMG 24594T) for which we propose the name Schleiferia thermophila gen nov., sp. nov. We also propose the family Schleiferiaceae fam. nov. to accommodate this new genus.

Hydrotalea sandarakina sp. nov., isolated from a hot spring runoff, and emended descriptions of the genus Hydrotalea and the species Hydrotalea flava

Two bacterial isolates, designated AF-51(T) and AF-50, with an optimum growth temperature of about 45 °C and an optimum pH for growth between 6.0 and 6.5, were recovered from a hot spring in the Furnas, Área da Fonte 1825, on the Island of São Miguel in the Azores. Based on 16S rRNA gene sequence analysis, these strains were related most closely to the type strain of Hydrotalea flava at a pairwise similarity of 95.7%. The two strains were orange-pigmented and formed non-motile, rod-shaped cells that stained Gram-negative and were aerobic and oxidase- and catalase-positive. The major fatty acids were iso-C(15:0), iso-C(17:0) 3-OH and iso-C(16:0). The major respiratory quinone was menaquinone 7. Based on phylogenetic, physiological and biochemical characteristics, these strains from the Azores are considered to represent a single novel species of the genus Hydrotalea, for which the name Hydrotalea sandarakina sp. nov. is proposed. The type strain is AF-51(T) (=DSM 23241(T)=LMG 25526(T)). We provide emended descriptions of the genus Hydrotalea and of H. flava to reflect new results obtained in this study.

Diversity, biological roles and biosynthetic pathways for sugar-glycerate containing compatible solutes in bacteria and archaea

A decade ago the compatible solutes mannosylglycerate (MG) and glucosylglycerate (GG) were considered to be rare in nature. Apart from two species of thermophilic bacteria, Thermus thermophilus and Rhodothermus marinus, and a restricted group of hyperthermophilic archaea, the Thermococcales, MG had only been identified in a few red algae. Glucosylglycerate was considered to be even rarer and had only been detected as an insignificant solute in two halophilic microorganisms, a cyanobacterium, as a component of a polysaccharide and of a glycolipid in two actinobacteria. Unlike the hyper/thermophilic MG-accumulating microorganisms, branching close to the root of the Tree of Life, those harbouring GG shared a mesophilic lifestyle. Exceptionally, the thermophilic bacterium Persephonella marina was reported to accumulate GG. However, and especially owing to the identification of the key-genes for MG and GG synthesis and to the escalating numbers of genomes available, a plethora of new organisms with the resources to synthesize these solutes has been recognized. The accumulation of GG as an 'emergency' compatible solute under combined salt stress and nitrogen-deficient conditions now seems to be a disseminated survival strategy from enterobacteria to marine cyanobacteria. In contrast, the thermophilic and extremely radiation-resistant bacterium Rubrobacter xylanophilus is the only actinobacterium known to accumulate MG, and under all growth conditions tested. This review addresses the environmental factors underlying the accumulation of MG, GG and derivatives in bacteria and archaea and their roles during stress adaptation or as precursors for more elaborated macromolecules. The diversity of pathways for MG and GG synthesis as well as those for some of their derivatives is also discussed. The importance of glycerate-derived organic solutes in the microbial world is only now being recognized. Their stress-dependent accumulation and the molecular aspects of their interactions with biomolecules have already fuelled several emerging applications in biotechnology and biomedicine.

Rhodothermus profundi sp. nov., a thermophilic bacterium isolated from a deep-sea hydrothermal vent in the Pacific Ocean

Nine thermophilic strains of aerobic, non-sporulating, heterotrophic bacteria were isolated after enrichment of chimney material sampled from a deep-sea hydrothermal field at a depth of 2634 m on the East-Pacific Rise (1 °N). The bacteria stained Gram-negative. They were rod-shaped and measured approximately 0.5 μm in width and 1.5–3.5 μm in length. They grew at 55–80 °C, pH 6–8 and 1–6 % NaCl. Optimal growth was observed at 70–75 °C, pH 7.0 and 1–3 % NaCl. The organisms were identified as members of the genus Rhodothermus, having a 16S rRNA gene similarity of 98.1 % with Rhodothermus marinus DSM 4252T. The novel isolates differed morphologically, physiologically and chemotaxonomically from R. marinus, e.g. in lack of pigmentation, response to hydrostatic pressure, maximum growth temperature and DNA G+C content. DNA–DNA hybridization revealed a reassociation value of 37.2 % between strain PRI 2902T and R. marinus DSM 4252T, which strongly suggested that they represent different species. Furthermore, AFLP fingerprinting separated the novel strains from R. marinus reference strains. It is therefore concluded that the strains described here should be classified as representatives of a novel species for which the name Rhodothermus profundi sp. nov. is proposed; the type strain is PRI 2902T (=DSM 22212T =JCM 15944T).

Complete genome sequence of Rhodothermus marinus type strain (R-10)

Rhodothermus marinus Alfredsson et al. 1995 is the type species of the genus and is of phylogenetic interest because the Rhodothermaceae represent the deepest lineage in the phylum Bacteroidetes. R. marinus R-10^T is a Gram-negative, non-motile, non-spore-forming bacterium isolated from marine hot springs off the coast of Iceland. Strain R-10^T is strictly aerobic and requires slightly halophilic conditions for growth. Here we describe the features of this organism, together with the complete genome sequence, and annotation. This is the first complete genome sequence of the genus Rhodothermus, and only the second sequence from members of the family Rhodothermaceae. The 3,386,737 bp genome (including a 125 kb plasmid) with its 2914 protein-coding and 48 RNA genes is part of the Genomic Encyclopedia of Bacteria and Archaea project.

Molecular and biochemical characterization of a novel xylanase from the symbiotic Sphingobacterium sp. TN19

A xylanase-encoding gene, designated xynA19, was cloned from Sphingobacterium sp. TN19--a symbiotic bacterium isolated from the gut of Batocera horsfieldi larvae--and expressed in Escherichia coli BL21 (DE3). The full-length xynA19 (1,155 bp in length) encodes a 384-residue polypeptide (XynA19) containing a predicted signal peptide of 24 residues and a catalytic domain belonging to glycosyl hydrolase family 10 (GH 10). The deduced amino acid sequence of XynA19 is most similar (53.1% identity) to an endo-1,4-beta-xylanase from Prevotella bryantii B(1)4. Phylogenetic analysis of GH 10 Bacteroidia xylanases indicated that GH 10 xylanases from Sphingobacteria were separated into two clusters, and XynA19 is more closely related to the xylanases of Bacteroidia from gut or rumen than to those of Flavobacteria and Sphingobacteria from other sources. Recombinant XynA19 (r-XynA19) showed apparent optimal activity at pH 6.5 and 45 degrees C. Compared with thermophilic and mesophilic counterparts, r-XynA19 was more active at low temperatures, retaining >65% of its maximum activity at 20-28 degrees C and approximately 40% even at 10 degrees C, and modeling indicated that XynA19 has fewer hydrogen bonds and salt bridges. These properties suggest that XynA19 has various potential applications, especially in aquaculture and the food industry.

Balneola vulgaris gen. nov., sp. nov., a member of the phylum Bacteroidetes from the north-western Mediterranean Sea

A novel aerobic, Gram-negative bacterium, named 13IX/A01/164T, was isolated from surface waters in the coastal north-western Mediterranean Sea. Cells were motile, straight rods, 2.5 μm long and 0.2 μm wide, and formed orange colonies on marine agar medium. The G+C content of the genomic DNA of strain 13IX/A01/164T was 42 mol%. Phylogenetic analysis of the 16S rRNA gene sequence placed the strain in the phylum Bacteroidetes within the family Crenotrichaceae. On the basis of 16S rRNA gene sequence comparison and physiological and biochemical characteristics, this isolate represents a novel species of a new genus, for which the name Balneola vulgaris gen. nov., sp. nov. is proposed. The type strain of Balneola vulgaris is 13IX/A01/164T (=DSM 17893T=CIP 109092T=OOB 256T).

Rhodothermus marinus: physiology and molecular biology

Rhodothermus marinus has been the subject of many studies in recent years. It is a thermohalophilic bacterium and is the only validly described species in the genus Rhodothermus. It is not closely related to other well-known thermophiles and is the only thermophile within the family Crenotrichaceae. R. marinus has been isolated from several similar but distantly located geothermal habitats, many of which are subject to large fluctuations in environmental conditions. This presumably affects the physiology of R. marinus. Many of its enzymes show optimum activity at temperatures considerably higher than 65 degrees C, the optimum for growth, and some are active over a broad temperature range. Studies have found distinguishing components in the R. marinus electron transport chain as well as in its pool of intracellular solutes, which accumulate during osmotic stress. The species hosts both bacteriophages and plasmids and a functional intein has been isolated from its chromosome. Despite these interesting features and its unknown genetics, interest in R. marinus has been mostly stimulated by its thermostable enzymes, particularly polysaccharide hydrolysing enzymes and enzymes of DNA synthesis which may be useful in industry and in the laboratory. R. marinus has not been amenable to genetic analysis until recently when a system for gene transfer was established. Here, we review the current literature on R. marinus.

Intraspecific comparative analysis of the species Salinibacter ruber

Salinibacter ruber is the first extremely halophilic member of the Bacteria domain of proven environmental relevance in hypersaline brines at or approaching NaCl saturation, that has been brought to pure culture. A collection of 17 strains isolated from five different geographical locations (Mallorca, Alicante, Ebro Delta, Canary Islands, and Peruvian Andes) were studied following the currently accepted taxonomic approach. Additionally, random amplification of genomic DNA led to the phenetic analysis of the intraspecific diversity. Altogether the taxonomic study indicated that S. ruber remained highly homogeneous beyond any geographical barrier. However, genomic fingerprints indicated that populations from different isolation sites could still be discriminated.

The bacterium Thermus thermophilus, like hyperthermophilic archaea, uses a two-step pathway for the synthesis of mannosylglycerate

The biosynthetic pathway for the synthesis of the compatible solute alpha-mannosylglycerate (MG) in the thermophilic bacterium Thermus thermophilus HB27 was identified based on the activities of recombinant mannosyl-3-phosphoglycerate synthase (MPGS) (EC 2.4.1.217) and mannosyl-3-phosphoglycerate phosphatase (MPGP) (EC 3.1.3.70). The sequences of homologous genes from the archaeon Pyrococcus horikoshii were used to identify MPGS and MPGP genes in T. thermophilus HB27 genome. Both genes were separately cloned and overexpressed in Escherichia coli, yielding 3 to 4 mg of pure recombinant protein per liter of culture. The molecular masses were 43.6 and 28.1 kDa for MPGS and MPGP, respectively. The recombinant MPGS catalyzed the synthesis of alpha-mannosyl-3-phosphoglycerate (MPG) from GDP-mannose and D-3-phosphoglycerate, while the recombinant MPGP catalyzed the dephosphorylation of MPG to MG. The recombinant MPGS had optimal activity at 80 to 90 degrees C and a pH optimum near 7.0; MPGP had maximal activity between 90 and 95 degrees C and at pH 6.0. The activities of both enzymes were strictly dependent on divalent cations; Mn(2+) was most effective for MPGS, while Mn(2+), Co(2+), Mg(2+), and to a lesser extent Ni(2+) activated MPGP. The organization of MG biosynthetic genes in T. thermophilus HB27 is different from the P. horikoshii operon-like structure, since the genes involved in the conversion of fructose-6-phosphate to GDP-mannose are not found immediately downstream of the contiguous MPGS and MPGP genes. The biosynthesis of MG in the thermophilic bacterium T. thermophilus HB27, proceeding through a phosphorylated intermediate, is similar to the system found in hyperthermophilic archaea.

Phylogenetic characterization of microbial mats and streamers from a Japanese alkaline hot spring with a thermal gradient

Dense microbial mats and streamers of various colors developed in an alkaline-hot spring water at 48-76 degrees C and ~0.077 mm sulfide in Nakabusa, Japan. The microbial community structures with a thermal gradient were compared by denaturing gradient gel electrophoresis (DGGE) analysis of the PCR-amplified 16S ribosomal RNA gene fragments. The sequence analysis revealed that a predominant cyanobacterial DGGE band phylogenetically related to Synechococcus elongatus was detected only from green mats at 48 degrees C. Four DGGE bands were detected commonly from green mats at 48 degrees C, orange mats at 58 degrees C and brown mats at 60 degrees C. The sequence analysis revealed that these were phylogenetically related to Chloroflexaceae group, Rhodothermus group, a candidate division OP10, and an unclassified bacterium. On the other hand, Aquificae-, Thermodesulfobacteria-, Thermus group-, and Crenarchaeota-like sequences were detected as a predominant component of DGGE profiling from the streamers only at temperatures over 66 degrees C, but no phototrophic bacterial bands were detected. Thus, the microbial community structure above 60 degrees C was drastically different from that at the lower temperatures. After the addition of hydrogen into in vitro gray streamers with in situ spring water, sulfide production markedly occurred in the presence of ambient sulfate at 66 degrees C. This result suggests that in situ sulfide is partly produced by Thermodesulfobacteria-like sulfate-reducing bacteria in the streamers.